90 PR0CEED1>"GS OF THE 



proof of such an occurrence ; for, logically at least, it was al\va)''s 

 possible to invert a factorial expression and to represent a 

 supposed addition as the loss of an inhibiting factor. 



Px'of. Bateson vA'as followed hy Prof. J. B. Farmer and 

 Mr. P. L. de Vilmorin ; then Dr. Gates said : — 



Let me say, in the first place, that I heartily agree with Dr. Lotsy 

 that species may and do frequently originate through crossing. 

 There is abundant evidence of this in Q^nofhera and in various 

 other cases, evidence which Mendelians have, if I understand 

 tliein rightly, been inclined until quite recently to deny. Tl)e 

 question at issue is, then, whether this is the only method by 

 which new forms arise. 



I believe we will also agree with Dr. Lotsy that the individual, 

 and not the species, is the real organic unit. Had Dr. Lotsy 

 adhered to this thesis, I might, perhaps, have been able to agree 

 with him to the end. But he immediately discards this idea, and 

 adoptsthe conception that the genotype of Johannsen is a constant, 

 immovable, and eternal unit. The genotype or pure line is, 

 however, only the offspring of a relatively pure individual. I 

 have grown scores of such races in (Enothera, and they differ 

 from each other in every conceivable manner and to every 

 conceivable degree. By selfing individuals in successive genera- 

 tions innumerable genotypes or (as I prefer to call them) biotypes 

 may be obtained, which differ from each other in smaller and 

 smaller details. The biotype is, therefore, merely a concept, like 

 the species, only varjing within narrower limits. 



The work of Jennings with Paramecium has shown that pure 

 lines may be isolated by selection, differing from each other con- 

 stantly by fractious of a micron in average length. He specifically 

 points out, however, that these differences are only relatively con- 

 stant, and that by continued selection within a pure line races 

 may be obtained which differ from each other less and less, down 

 to the limits of accurate measurement. Continued selection and 

 pure-line breeding within a species or a pui'e line multiplies the 

 number of races and continually decreases their variability, unless 

 and until (and this is a fundamental point of difference between 

 Dr. Lotsy and myself) a germinal change occurs. 



We may then inquire, what is the justification for Dr. Lotsy's 

 dogmatic assertion that there is no such thing as a germinal 

 change? In this sweeping denial he far outdoes the Mendelians 

 themselves, and succeeds in reducing Mendelism as a philosophy 

 of evolution to a reduciio ad absurdum. We have been accus- 

 tomed to being asked by the Mendelian School to believe that all 

 evolution " from Amoeba to Man," or in any other direction you 

 may choose to consider it, has taken place by the " loss of unit 

 factors," or, as I would prefer to say, by negative mutations. 

 Thus, if a race of guinea-pigs is obtained, having six toes instead 

 of five, we are asked to believe that this race has not suffered a 

 germinal change, far less has it gained anything. jS"o, it has 



